This application is related to application Ser. No. 021,454, filed Mar. 19, 1979, entitled "Four Pole Wave Wound Direct Current Machine With Multi-Turn Armature Coils", now U.S. Pat. No. 4,270,065, issued May 26, 1981. The instant application relates to a dynamoelectric machine with an armature wound with lap windings consisting of multiple open turn coils.
For dynamoelectric direct current machines, there is a tendency for excessive current to flow in armature windings having only a single turn. Such dynamoelectric machines are often used in such applications as providing motive power for material handling equipment, using high voltage battery packs, and often used at relatively low speeds. One common method for limiting the current in such armature windings is to form windings with a plurality of turns. An armature of this type for a D.C. motor is illustrated, for example, in U.S. Pat. No. 3,506,864 which is directed to winding an armature with a plurality of turns extending betwen two spaced slots in a laminated core.
This patent is directed to closed-turn windings, which are practical only with thin flexible wire having a round cross section. Such windings may be made either by winding a thin wire repeatedly through a pair of armature slots in the manner disclosed in U.S. Pat. No. 3,506,864, or by bundling wires together in a loop, binding them together, and subsequently installing the assembled coil in armature slots. Such a coil is disclosed in the treatise by A. S. Langsdorf entitled, "Principles of Direct-Current Machines," fifth edition, published 1940, by McGraw-Hill Book Company, (New York & London), especially pages 325, 327, 344, and 345. Similar information may be found in the sixth edition of this treatise, published in 1959, at page 50. Such windings, being formed with closed windings, are impractical with larger wire, or with wire of a square cross section. As can be seen, such coils are formed of copper wire, in a plane. Armatures have radial slots. The copper wire, having a low yield point can be easily spread to reach the entrances of the radial armature slots. Then, the coil must be compressed, since the bottoms of the armature slots are at a lesser spacing than the tops. The copper wire cannot be distorted far enough to reach its yield point, and thus elastically resists lying properly at the bottom of the armature slots. While it is possible to retain such wires with wedges and the like, this yields a motor with additional pieces, each presenting another possible mode of failure and further difficulties and expense in assembling a motor. If many turns of thin wire are bundled together, this approach may be feasible, since the wires slip with respect to each other, and the friction between wires in the bundled coil retains its position after small movements that do not distort the copper wire to its yield point. However, this technique will not work with square wire, due both to the reduced surface area in contact, and the fact that square wire is wound in one plane, and resists being twisted out of the plane to fit in the radially-extending armature slots.
Heretofore, when the advantages of square conductors were desired, yielding a machine with more efficiency, since the armature slots are completely filled, as distinguished from having perhaps twenty-five percent or more air space, it was necessary to either limit each winding to a single open turn in order to place the conductor in the armature slot, it being pulled tightly towards the bottom of the slot by the connections to the commutator, or to form each winding in several sections which were welded or soldered together to form a continuous conductor. This greatly increases the complexity and cost of manufacturing the armature, and again yields a winding with a plurality of connections, each presenting a possible failure point of such an armature in use.
The prior art has suggested that the number of windings may be increased by doubling the number of windings in each armature core slot, and suggested methods of reducing the number of commutator slots by modifying the windings in various types of machines. However, the prior art has not disclosed a workable structure for implementing multiple open turn lap windings using wire large enough to be self-supporting, and having a large enough cross sectional area to require significant force both to cause the material to reach its yield point when being bent, and to maintain in position when the material is below its yield point.